5 # (feature name) => (internal name, used in %^H)
7 switch => 'feature_switch',
12 state => "feature_state",
15 my %feature_bundle = (
16 "5.10" => [qw(switch ~~ say err state)],
20 # Here are some notes that probably shouldn't be in the public
21 # documentation, but which it's useful to have somewhere.
23 # One side-effect of the change is that C<prototype("CORE::continue")>
24 # no longer throws the error C<Can't find an opnumber for "continue">.
25 # One of the tests in t/op/cproto.t had to be changed to accommodate
26 # this, but it really shouldn't affect real-world code.
29 # - sort out the smartmatch semantics
30 # - think about versioned features (use switch => 2)
36 feature - Perl pragma to enable new syntactic features
40 use feature qw(switch say);
42 when (1) { say "\$foo == 1" }
43 when ([2,3]) { say "\$foo == 2 || \$foo == 3" }
44 when (/^a[bc]d$/) { say "\$foo eq 'abd' || \$foo eq 'acd'" }
45 when ($_ > 100) { say "\$foo > 100" }
46 default { say "None of the above" }
51 It is usually impossible to add new syntax to Perl without breaking
52 some existing programs. This pragma provides a way to minimize that
53 risk. New syntactic constructs can be enabled by C<use feature 'foo'>,
54 and will be parsed only when the appropriate feature pragma is in
57 =head2 The 'switch' feature
59 C<use feature 'switch'> tells the compiler to enable the Perl 6
60 given/when construct from here to the end of the enclosing BLOCK.
62 See L<perlsyn/"Switch statements"> for details.
64 =head2 The '~~' feature
66 C<use feature '~~'> tells the compiler to enable the Perl 6
67 smart match C<~~> operator from here to the end of the enclosing BLOCK.
69 See L<perlsyn/"Smart Matching in Detail"> for details.
71 =head2 The 'say' feature
73 C<use feature 'say'> tells the compiler to enable the Perl 6
74 C<say> function from here to the end of the enclosing BLOCK.
76 See L<perlfunc/say> for details.
78 =head2 the 'err' feature
80 C<use feature 'err'> tells the compiler to enable the C<err>
81 operator from here to the end of the enclosing BLOCK.
83 C<err> is a low-precedence variant of the C<//> operator:
84 see C<perlop> for details.
86 =head2 the 'dor' feature
88 The 'dor' feature is an alias for the 'err' feature.
90 =head2 the 'state' feature
92 C<use feature 'state'> tells the compiler to enable C<state>
93 variables from here to the end of the enclosing BLOCK.
95 =head1 FEATURE BUNDLES
97 It's possible to load a whole slew of features in one go, using
98 a I<feature bundle>. The name of a feature bundle is prefixed with
99 a colon, to distinguish it from an actual feature. At present, the
100 only feature bundle is C<use feature ":5.10">, which is equivalent
101 to C<use feature qw(switch ~~ say err state)>.
109 Carp->import("croak");
110 croak("No features specified");
113 my $name = shift(@_);
114 if ($name =~ /^:(.*)/) {
115 if (!exists $feature_bundle{$1}) {
117 Carp->import("croak");
118 croak(sprintf('Feature bundle "%s" is not supported by Perl %vd',
121 unshift @_, @{$feature_bundle{$1}};
124 if (!exists $feature{$name}) {
126 Carp->import("croak");
127 croak(sprintf('Feature "%s" is not supported by Perl %vd',
130 $^H{$feature{$name}} = 1;
137 # A bare C<no feature> should disable *all* features
139 delete @^H{ values(%feature) };
145 if ($name =~ /^:(.*)/) {
146 if (!exists $feature_bundle{$1}) {
148 Carp->import("croak");
149 croak(sprintf('Feature bundle "%s" is not supported by Perl %vd',
152 unshift @_, @{$feature_bundle{$1}};
155 if (!exists($feature{$name})) {
157 Carp->import("croak");
158 croak(sprintf('Feature "%s" is not supported by Perl %vd',
162 delete $^H{$feature{$name}};